The present invention relates to a process for the production of an ether-rich additive for gasoline and, more particularly, the production of ter amyl methyl ether (TAME) from FCC light hydrocarbon streams containing nitriles.
MTBE, TAME or mixtures thereof are used extensively as fuel extenders and octane value improving agents in the production of unleaded gasoline. Generally, but for the inclusion of such fuel extenders and octane value improving agents, acceptable octane values can only be obtained by varying the compounding additives in the gasoline, that is, increasing the lead content of the gasoline. The desirability of lead free gasolines is clearly recognized. Lead additives in gasolines result in the emission of pollutants in exhaust gases from internal combustion engines thereby contributing to overall environmental pollution. The employment of substitutes for lead in gasoline compounds which improve the octane value of the gasoline will lead to a cleaner burning gasoline thereby improving air quality and the overall environmental condition.
Currently, MTBE is frequently selected as the octane value improving additive over TAME due to processing considerations; however, TAME is a highly desirable octane value improving additive.
There are many processes developed in the prior art for producing MTBE (methyl t-butyl ether) and TAME (methyl t-amyl ether). Typical etherification processes are disclosed in U.S. Pat. Nos. 5,001,292; 4,925,455; 4,827,045; and 4,830,635 to Harandi et al.Other known processes include that disclosed in U.S. Pat. No. 4,025,989 to Hagan et al. For the most part, these known processes for preparing ethers as additives for gasoline comprise reacting a primary alcohol, such as methanol, with an olefin having a double bond on a tertiary carbon atom, such as, isobutylene and isoamylenes. It is known in the prior art to react the alcohol and the olefin in the presence of a catalyst. Suitable known catalysts include Lewis acids (sulfuric acid) and organic acids (alkyl and aryl sulfonic acids). A particularly suitable catalyst for these reactions are ion exchange resins in their acid form of the type marketed under the trademark "AMBERLIST 15" which is a trademark of Rohm and Haas or Bayer product K2631. While many hydrocarbon feedstocks may be used for the manufacture of MTBE and TAME it is particularly useful in the petroleum refining operation to process TAME from light hydrocarbon streams resulting from fluid catalytic cracking (FCC) refinery operations. When processing FCC hydrocarbon streams under etherification conditions to form TAME it has been found that the catalysts used in the process are rapidly poisoned, that is, the catalysts are deactivated. As the catalyst materials used in known processes are relatively expensive, the foregoing problem of catalyst deactivation leads to not only process inefficiency but also substantial increases in processing costs. None of the prior art processes, and particularly none of the U.S. Patents discussed above, deal with the aforesaid problem or suggest solutions thereto.
Naturally, it would be highly desirable to provide a process for the conversion of hydrocarbon streams, particularly light naphtha hydrocarbon streams from FCC refinery processes, to TAME which overcome the problems of catalyst poisoning as discussed above.
Accordingly, it is the principal object of the present invention to provide a process for the conversion of liquid light hydrocarbon streams to TAME in an efficient and economic manner.
It is a particular object of the present invention to provide a process as aforesaid wherein the poisoning of the catalysts used in the etherification process is inhibited.
It is a further object of the present invention to provide a process as aforesaid wherein the liquid light hydrocarbon feedstock fed to the etherification zone is pretreated for processing under etherification conditions in the presence of the catalyst.
Further objects and advantages of the present invention will appear hereinbelow.